The Things I've Seen: The Doodson-Lege Tide Predicting Machine

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The Independent Travel
IT struck me that a hilltop was an odd place for an oceanographic research station. I wondered if the station's builders knew something I didn't. But its position turned out simply to be a result of evolution.

Bidston Hill, in the Wirral, has for many years had associations with the sea. A system of hilltop flags was once used to notify Liverpool shipowners of the arrival of their ships in the bay. The Observatory at Bidston Hill was built in 1866. The equipment made possible astronomical and meteorological work. The observatory began to work in tandem with the Liverpool Tidal Institute, which eventually moved to the same site. And slowly the tidal work began to predominate.

I had come to see one of the most important results of this work. The Doodson-Lege Tide Predicting Machine was in daily use from 1949 to the early Sixties. It stands silent now, but at the peak of its operations, in 1955, it prepared full annual tidal predictions for 160 ports around the world. The entire process was mechanical. Forty two interconnected pulley wheels on the machine each represented a tidal component, with such names as 'Principal lunar semi-diurnal' and 'solar annual'. All these constituents were drawn together by the machine and its operator to produce tidal predictions. It took one and a half days to run a year of tidal predictions for a port. Similar operations using a modern computer take about one minute.

The Doodson-Lege Tide Predicting Machine is at the Proudman Oceanographic Laboratory, Bidston Hill. Ordnance Survey grid reference SJ 2889.

(Photograph omitted)

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